The development of display industry at present leads to an increasingly increased demand on characteristics of thin film transistors (TFTs), it is required by high-resolution liquid crystal displays (LCDs) and large-size active matrix organic light-emitting diode displays (AMOLEDs) that TFT devices of an array substrate have a larger on-state current and a very high on-off ratio, and therefore, higher carrier mobility is better for TFT devices. However, mobility of TFTs at present remains lower than expected generally (being about 10 cm2 V−1 S−1), and cannot meet the needs of progressive development of technology.